1. The Field of the Invention
This invention relates generally to a knee support device. More particularly, this invention relates to a device which supports and stabilizes the knee, including the patella, to resist abnormal lateral subluxation of the patella during motion of the knee joint.
2. The Background Art
Anterior knee pain (i.e., pain in the forward part of the knee), is one of the most common complaints that cause patients to consult a knee specialist. A frequent cause of such pain is malalignment of the patellofemoral joint which is often associated with instability of the patella (knee cap).
Patellar instability usually occurs laterally (i.e., in a direction away from the other leg), and is referred to as "patellar subluxation," "patellar dislocation," or "patellar hypermobility." In a patient with this knee disorder, the muscles and ligaments which hold the patella in its proper position in the knee are malaligned, very loose or lax. This condition is caused either by developmental abnormalities (generally in younger children), or by injuries to the muscles and/or ligaments attached to the patella. Because of the very loose placement of the patella in this condition, the patella may become misoriented relative to its normal position during flexion/extension rotation of the knee joint (i.e., during normal "bending" of the leg at the knee joint). Such misorientation usually occurs when the joint is extended under stress, such as during strenuous physical activity in which the knee is carrying an increased load while it is rotating.
Not only can patellar subluxation cause severe pain, the knee is also more prone to give way (buckle) under the strain of a load placed thereon when the patella is not properly oriented. Moreover, continued or frequent abnormal displacements of the patella can cause severe degeneration of the patella and the surrounding knee structure.
The conservative treatment of patellar instability often includes muscle rehabilitation, medication, and/or activity modification. In addition, those skilled in the art have developed numerous types of knee braces to assist in the treatment of patellar instability. Such braces range from very simple to quite complex and have been successful in the treatment of patellar instability to varying degrees.
A simple knee sleeve is often used to provide static patellar support. The sleeve is generally made of an elastic material and has an opening through which the knee cap protrudes. When thus positioned, the sleeve exerts a static force on the knee to assist in maintaining the patella in proper alignment.
Another prior art bracing device comprises an infrapatellar strap. The strap is wrapped around the knee so as to support the patella during motion of the knee joint.
Still another prior art device comprises a bracing pad held in a lateral position with respect to the patella by means of an elastic sleeve and a plurality of elastic straps. This device is intended to apply a medially displacing force to the patella (i.e., a force in a direction toward the other leg), and maintain constant pressure during flexion, extension, and rotation of the knee.
Despite the limited success of some prior art devices in treating patellar instability, the exact function of many of the devices is unclear. For example, some prior art devices may help alleviate pain for a variety of reasons. The warmth the device provides to the knee may be therapeutic. Similarly, sensory feedback may be altered, thereby reducing the patient's awareness of discomfort. Likewise, a possible alteration in circulation is another potential effect of many devices. These nonspecific mechanisms might help explain the potential effectiveness of some prior art patellar bracing devices.
Many existing brace devices are also subject to shifting on the user's knee during movement of the knee joint. Of course, such shifting may cause the brace to become misaligned, thereby significantly reducing the functional effectiveness of the brace.
In addition, the physiology of the knee is such that the patella slips deeply into the cavity provided for it when the knee joint is in hyperextension. In such cases, the structure of existing brace devices is such that the patella may slip below the bracing member and rotate thereunder. The bracing device is thereby rendered largely ineffective.
Further, the mechanical function of existing devices seems limited to applying a medial force to the lateral aspect of the patella in patients with patellar tracking problems. While this function is believed to be based upon sound biomechanical principles, it treats only one cause of patellar instability. There is no known evidence that this function is applicable in treating any other causes. Consequently, there remains a need for a bracing device which more completely enhances and facilitates patellar stability.